This invention relates to a recording sheet and more particularly to an improved color developer sheet which reacts with certain nearly colorless dyes to form an intensely colored image.
Recording sheets comprising isolated discrete droplets of an oil solution containing a substantially colorless dye and a separate composition which reacts with the dye to develop color are well known. An example is commonly referred to as carbonless copy paper. Such products comprise two or more sheets, one or more having a coated back (CB) containing a plurality of isolated discrete droplets of oil containing one or more dissolved dyes, and one or more sheets having a coated front (CF) containing a layer of color developer mixed with a binder. When the sheets are placed in face to face contact, marking pressure on the top sheet releases the dye in the CB which is developed on contact with the developer in the CF. Such developer compositions generally employ as an active ingredient a phenolic resin material, a clay or clay-like material such as montmorillonite clay, acid clay, activated clay, zeolite, or bentonite, or an organic acid. Some improvement in color intensity in phenolic resin-based developer materials may be obtained by neutralizing certain of the phenolic hydroxyl groups with metal ions such as zinc ions. The prior art literature also reports that metal salts of certain aromatic carboxylic acids may be used to improve color intensity in CF compositions.